1. Field of the Invention
The invention concerns a device supplying a discharge lamp of a motor vehicle headlight.
The invention concerns more particularly an electrical supply device for a discharge lamp of a motor vehicle headlight that comprises:
an electric current source;
an electronic module for converting source electric current into supply electric current for the discharge lamp;
a housing that encloses the electronic module and is produced from/comprises an electrically conductive material so as to form electromagnetic shielding, in particular for attenuating the intensity of electromagnetic radiation emitted by the electronic module;
an electrical connection harness that is intended to electrically connect the electronic conversion module with the discharge lamp;
an envelope produced from/comprising an electrically conductive material that surrounds the connection harness so as to form electromagnetic shielding, in particular in order to attenuate the intensity of electromagnetic radiation emitted by the connection harness;
the housing and envelope being electrically connected to a common reference electrical potential.
2. Description of the Related Art
In the automobile industry, use is being made more and more of headlights equipped with discharge lamps, such as xenon lamps, in particular for their light yield and for their longevity.
This type of lamp requires a high-voltage AC electric current supply. In order to control the supply of electric current to the lamp, the headlight comprises an electrical supply device that is equipped with an electronic conversion module, normally referred to as “ballast”, which supplies, from a battery voltage of the motor vehicle, high alternating voltages that are adapted to the type of discharge lamp used.
Discharge lamps may emit a large quantity of electromagnetic radiation, the effect of which is undesirable both with regard to the security of operation of the other electronic circuits of the vehicle and on the radio environment in which the vehicle is travelling.
To remedy this drawback, it is known how to take several measures referred to as “EMC”, an acronym meaning “electromagnetic compatibility”, separately or in combination according to circumstances, when the electrical supply device of the discharge lamp of the headlight is designed.
According to a first measure, it is known that the electromagnetic radiation is mainly emitted by the connectors, by the connection harness, the length of which may in some cases be high, and by certain electronic equipment such as the ballast. This first measure for reducing the electromagnetic radiation emissions consist, as is known, of executing a shielding of the supply harness to the electric lamp and the ballast as well as, where necessary, its connectors.
According to a second measure, the shielding of the lamp, of the ballast and of the supply harness or harnesses must be connected to a common reference electrical potential so that the various shieldings cannot vary in voltage during use and thus change into parasitic radiating structures.
The problem at the basis of the invention consists of ensuring that the shielding of the harness connecting the ballast to the discharge lamp is correctly connected to the reference potential so as to comply with the constraints relating to the electromagnetic standards.
It is known how to electrically connect the reference potential to the housing of the ballast and then to connect the shielding of the connection harness in series with the shielding of the ballast.
However, it was found that, in some configurations, such an interconnection did not make it possible to attenuate the parasitic electromagnetic radiation in a satisfactory manner.